For the achievement:
It seems like you lot thriving
While playing on Very Sweet Mode watch all five female characters in their new erotic costumes.
All you have to do is put the difficulty on Very Sweet Mode and whenever a cut scene plays with a female character, don't skip it.
Can you just rest on the armchair and play all the cut scenes by "Dreaming" ? Will that unlock the achievement? Was going to try that out, if no one knows I'll post if I got the achievement by doing so.
Just got the achievement:
すべてのちょいエロコスチュームを堪能した - 20 GS
After beating Death Metal on Very Sweet and returning to your hotel room, you can rest on your armchair and Dream all the cutscenes including women to unlock the achievement. I just got done watching all the Episode 1 cut scenes that included women, Silvia (after beating Death Metal) Shinobu ep. 1, Holly Summers ep. 1, Bad Girl ep. 1, and Jeane ep. 1 and got the achievement.
So hopefully this helps out incase anyone doesn't want to play through it again on Very Sweet and then on Bitter as well.